1. Field of the Invention
The invention relates generally to the field of subsurface wellbore inspection using video. More specifically, the invention relates to apparatus and methods for video inspection and remediation during wellbore milling operations.
2. Background Art
Wellbore operations for wellbores drilled through the Earth's subsurface include milling. Milling is used for, among other purposes, providing a suitable upper surface to tools and equipment that have become lodged or placed in the wellbore so that such tools and equipment can be inspected, retrieved, and/or repaired while in the wellbore or retrieved from the wellbore using a retrieval tool or a repair device. Milling is also used to cut windows though the wall of pipe or casing disposed in the wellbore so that “lateral” wellbores can be drilled and “tied back” to the wellbore through which the window was milled. Milling is typically performed by coupling a suitable milling tool to the end of a pipe string (drill string, coil tubing or work string) that is then inserted into the wellbore to the place where the milling is to be performed. The drill string or pipe string is typically formed by threadedly coupling pipe segments (“joints” or “stands”) together end to end or with a continuous pipe conduit such as coil tubing. The milling tool may be rotated by rotating the pipe string, or by pumping fluid through an hydraulic motor coupled in the lower portion of the pipe string.
The success of milling operations is dependent to a large degree on the skill of the mill operator. This is because the mill operator must make inferences about the condition of the device being milled and the milling tool only from: (i) surface measurements of torque applied to the drill string or work string to which the mill is coupled; (ii) axial loading applied to the mill inferred from surface measurements of the suspended weight of the drill string or work string; and (iii) pressure of fluid being pumped through the drill string or work string.
In order for the wellbore operator to use the milled casing window or to attempt to retrieve or repair the milled tools and equipment, it is necessary to remove the drill string or work string from the wellbore, and to then attempt to insert tools and equipment through the milled window or to attempt to retrieve/repair the lodged tools and equipment by coupling suitable devices to the end of the drill string or work string. The drill string or work string is then reinserted into the wellbore with the suitable devices thereon. If the milling operation performed previously is incomplete, the wellbore operator will learn of such condition only when the devices fail to accomplish their purpose. It is then necessary for the wellbore operator to retrieve the drill string or work string, and resume milling operations. Repeated “tripping” the drill string or work string can be time consuming and expensive.
The speed at which milling operations proceed may depend on a number of conditions within the wellbore, one of which is the condition of the milling tool. If milling operations proceed at a slower rate than expected, or materially slow down during the course of milling operations, the wellbore operator may reasonably conclude that the milling tool is becoming worn and needs to be replaced. Replacing the milling tool requires tripping the pipe string. If it is determined that the milling tool was not worn, then the pipe string trip will have proven to be unnecessary.
It is desirable to have a device for inspecting a milled device within a wellbore and for inspecting a milling tool while it is disposed in the wellbore so that unnecessary pipe tripping can be reduced.